The camera and the gimbal are built into one unit for convenience, but they are two different things. You have a gimbal problem. Specifically, the Yaw encoder has a problem.
This would normally be a shop repair but it may be difficult to find a shop that can do the repair.
Did anything happen to the gimbal between the last time it worked and the first time it did not? Things like crash, long storage time, firmware updates, repairs, modifications or anything you can thing of?
You can also check that the connector marked "K" in the attached image is not loose or has wire damage.